The present invention relates to a method of controlling a transmission device of a motor vehicle power train in a situation termed braking. It also relates to a device implementing such a control method.
This method applies advantageously to automated transmission devices in particular Impulse Control Boxes termed BCI, Automatic Control Boxes termed BVA and Robotized Gear Boxes termed BVP, but also continuous-ratio transmissions, such as CVT (“Continuous Variable Transmission”), IVT (“Infinitely Variable Transmission”) and hybrid transmissions.
A motor vehicle automated transmission conventionally comprises a control block receiving one or more input parameters interpreting inter alia, the desire of the driver. Then, as a function of the value of these parameters, the control block delivers a control setpoint with a view to an application to the wheels of the motor vehicle.
An upgrade of such a control block has already been described in document FR-A-2827339, in the name of the Applicant. This document details a device for controlling the operating point of a power train. The control carried out by this device is a torque control applied to the wheels of the motor vehicle. As defined in document FR-A-2827339, the value of the torque to be applied to the wheels of the motor vehicle is calculated directly at the wheels of the motor vehicle.
The device of document FR-A-2827339 possesses a module for interpreting the desire of the driver called an IVC module.
The IVC module generates a torque setpoint to be applied to the wheels, destined for a block for optimization of the operating point OPF. The latter transmits said torque with a view to a torque control applied to the wheels of the motor vehicle. The OPF block simultaneously generates an engine revs setpoint on the basis of said torque applied to the wheels of the motor vehicle. This torque setpoint to be applied to the wheels of the motor vehicle is determined as a function of the desire of the driver, of the characteristics of the motor vehicle and of its environment, so as to best adapt the behavior of the motor vehicle, according to the driving situations.
In a braking situation, that is to say during the activation of the brake pedal of the motor vehicle, it is indispensable to adapt the torque setpoint applicable to the wheels of the motor vehicle, in such a way as to offer the driver optimal driving comfort as well as command of the acoustics of the power train. This adaptation must be performed during the braking phase but also during reacceleration, after said braking phase.
For example, for a motor vehicle equipped with an automatic transmission, in order to actuate the brake pedal, the driver must ease off the accelerator pedal. The automatic gearbox which was previously in a given gear, then shifts directly to the gear above on account of the conventional shifting laws of an automatic gearbox. It thus deprives the motor vehicle of engine brake. The shift to the gear above then causes an unpleasant sensation of boarding of the motor vehicle. In order to cause the shift to the lower gear, the driver must depress the accelerator pedal to the maximum, to benefit from the downshift function with a view to a reacceleration, termed the “kick-down” function.
A method is known in the prior art through document U.S. Pat. No. 5,514,051 filed by Porsche, said method consisting in adjusting driving parameters of the motor vehicle as a function of predefined parameters corresponding to a normal driving situation. When the motor vehicle is in a particular state, a braking state for example, a computer detects the deviation with respect to the normal driving situation and adjusts the driving parameters accordingly. This method is intended for motor vehicles equipped with an automatic transmission.
A method making it possible to maintain engine brake before reacceleration within the framework of motor vehicles equipped with a continuous variation gearbox termed a CVT box is likewise known through the document EP 0 280 757. A device allows a downshift of the transmission to be blocked so as to benefit from additional engine brake.
In document. FR-2 765 652 in the name of the applicant, it is proposed to produce a device for controlling downshifts in a braking situation for motor vehicles possessing a stepped-ratio transmission. This control makes it possible to shift directly to a lower gear if a particular operating regime is detected, a braking situation for example, then locks this lower gear as long as the particular regime is detected.
Finally, a device which makes it possible to preposition the operating point of the power train in a braking situation for example is known through the document FR-2 834 939 in the name of the applicant. One thus obtains a torque reserve allowing reacceleration out of the braking phase. The control setpoint is calculated as an engine torque.